What aggregates are and how they are made

Aggregate is the construction industry's word for the granular material that goes into concrete, asphalt, road bases and fill. The term covers sand, gravel, crushed stone and recycled material, and most people meet it only as a pile on a building site or a line on a delivery ticket. This page explains what aggregates are, how natural and crushed material differ, how it is taken from the ground and processed, and where it ends up. Production figures come from the United States, because the U.S. Geological Survey (USGS) publishes detailed public numbers, and they are labelled as American data throughout.

01What counts as an aggregate

The Kansas Geological Survey describes aggregate as a construction material that is hard and inert, meaning it does not react chemically with the materials around it, and that is used to make concrete, mortar, asphalt or similar products. It lists sand, gravel, crushed stone and lightweight aggregate under that one heading. The same publication estimates that the average American uses more than a million pounds of cement, sand, gravel and crushed stone over a lifetime, which says something about how ordinary and how heavy these materials are (Kansas Geological Survey, a 1997 circular).

Aggregates are sorted by particle size. In concrete work, the U.S. Federal Highway Administration (FHWA) training material defines coarse aggregate as material predominantly retained on a 4.75 mm sieve, which is a wire mesh used to sort particles by size, while fine aggregate is the sand-sized material that passes it (FHWA Highway Materials Engineering Course, Lesson 10). Other specifications use other cut-offs. The way a batch is spread across sizes is called its grading, and it has its own page on aggregate sizes and grading.

02Natural, crushed and recycled material

Natural sand and gravel start as rock that has been broken down by weathering. The Kansas Geological Survey explains that rocks are broken, ground up and rounded as rivers carry them along, which is why river gravel tends to look smooth. FHWA describes weathered natural sand in similar terms: very hard particles that are polished and rounded or semi-rounded, with few flat or elongated pieces. Those shapes are one reason natural sand is so common in concrete, a point taken up on the sand types and uses page.

Crushed stone is different. It starts as solid rock in a quarry, such as limestone, dolomite or granite, and is broken to size by machines. The USGS reports that, of the crushed stone produced in the United States in 2025, about 70 percent was limestone and dolomite and 14 percent was granite (USGS Mineral Commodity Summaries 2026: Stone (Crushed)). Freshly broken faces make crushed particles angular. FHWA notes that rough, angular particles need more water to make workable concrete than smooth, rounded ones, although the hardened strength of concrete generally rises with more angular coarse aggregate (FHWA-RD-97-148). Neither shape is simply better. Each suits particular jobs.

The two families overlap in practice. The USGS says crushed stone is often substituted for natural sand and gravel, especially in more densely populated parts of the eastern United States, and describes crushed stone as the dominant choice for construction aggregate overall (USGS Mineral Commodity Summaries 2026: Sand and Gravel (Construction)).

Recycled aggregate comes from crushing old asphalt and concrete. The USGS says road surfaces made of asphalt concrete and portland cement concrete were recycled on a limited but increasing basis in most American states, and in all 50 states in 2025, though the share of total aggregate supplied by recycled material remained very small. A separate manufactured category, lightweight aggregate, is made by heating crushed shale in a kiln until it swells, and it is used mainly in lightweight concrete and blocks (Kansas Geological Survey). Recycled material is covered in more detail on the recycled aggregates page.

03Getting material out of the ground

Crushed stone production begins with blasting. The U.S. Environmental Protection Agency (EPA) describes rock being loosened by drilling and blasting, then loaded by power shovel or front-end loader into haul trucks that carry it to the processing plant, with extraction techniques varying by deposit and location (EPA AP-42 Section 11.19.2, last revised in 2004).

Sand and gravel are won in several ways. The USGS names glacial deposits, river channels and river flood plains as the most important commercial sources. The Kansas circular describes small dry pits where front-end loaders fill trucks, as well as dredging. A river dredge suctions sand from the bed and sends it to a plant on the bank for washing and sorting, while a floodplain dredge floats on a pit that has filled with groundwater. Floodplain pits usually need the soil and rock above the deposit, called overburden, removed first, and such pits require reclamation when digging ends.

Offshore deposits are a further source. According to the USGS, use of offshore deposits in the United States is mostly restricted to beach erosion control and replenishment, whereas other countries routinely mine offshore deposits for onshore construction. How operations are permitted and monitored varies widely, and the how quarries are regulated page gives the general picture. What happens to a site afterward is covered under quarry rehabilitation and the environment.

04Crushing, screening and washing

Raw quarried rock is far too coarse and too varied to sell as it comes. The EPA's process description walks through the usual sequence. Quarried stone is dumped into a bin, and a feeder or screen separates large boulders from finer rock. Jaw, impactor or gyratory crushers do the first reduction, producing pieces normally 7.5 to 30 cm across. Cone crushers then typically reduce the stone to about 2.5 to 10 cm in a secondary stage, and a tertiary stage brings output to roughly 0.5 to 2.5 cm. After each stage, vibrating screens sort the material into product streams of different sizes, and anything too large goes back for another pass.

Some plants go further and make manufactured sand, defined by the EPA as a small-sized rock product with a maximum size of 0.5 cm. Finished sizes go to bins or stockpiles, or to other processing such as washing, air separators and classifiers. The EPA adds that stone washing is required in certain cases to meet particulate specifications.

Washing matters because fine clay and silt cling to larger particles. FHWA's course material notes that these fines are often removed only by washing, and that extra fine material raises the water a concrete mix needs, which can reduce long-term strength and durability. Even the dust left over from crushing has a use, since the Kansas Geological Survey says many producers collect it and sell it as agricultural lime.

Crushing and screening also raise dust, and the EPA says these processes can be significant sources of particulate emissions if uncontrolled. Plants that use water sprays to keep material damp can control much of that dust, the EPA says. The USGS adds that producers continue to address health and safety regulations, and industrial sand producers in particular cite rules on crystalline silica exposure. What public bodies actually say about silica dust is set out on the silica dust and quarry safety page. Rules and practice differ by country and by site, and a reader's own mine-safety or workplace-safety regulator has the final word on what applies to them.

05How much is produced

American figures show the scale. The USGS estimates that about 870 million tons of construction sand and gravel and about 1.5 billion tons of crushed stone were produced in the United States in 2025 (its data tables are in metric tons). Output was roughly flat for crushed stone against 2024 and slightly lower for sand and gravel, at 870 million tons compared with 880 million. The agency lists construction activity, infrastructure funding, housing starts and weather among the factors that move demand.

Estimated U.S. aggregate production, 2025

Material	Output	Operations
Construction sand and gravel	About 870 million tons	About 6,500 pits run by an estimated 3,400 companies
Crushed stone	About 1.5 billion tons	About 3,500 quarries run by an estimated 1,400 companies

These numbers apply to the United States only. The USGS states that no reliable production information is available for most other countries because of the wide variety of ways in which countries report sand and gravel, and crushed stone, production. A global total would therefore be a guess.

Aggregates are heavy and cheap per tonne, so they are rarely moved far. The USGS expects new pits and quarries to be located away from large population centers because of zoning and land-development pressures, which in turn can produce regional shortages and higher fuel costs. The Kansas circular makes the same point about transport cost, putting it at about $0.10 per ton per mile in the mid-1990s.

06What aggregates are used for

The USGS breaks down American use of construction sand and gravel as follows: an estimated 42 percent as aggregate in portland cement concrete, 20 percent for road base and coverings, 12 percent for construction fill, and 9 percent for asphalt and other bituminous mixtures. The remainder covers concrete products, drainage and riprap, filtration, golf course maintenance, landscaping, masonry sand, pea gravel, plaster and gunite sands, railroad ballast, snow and ice control and other minor uses.

Most crushed stone goes into construction as well. The USGS estimates that 72 percent was used as construction aggregate in 2025, mostly for road construction and maintenance, while 17 percent went to cement manufacturing, 6 percent to lime manufacturing and 1 percent to agriculture, with the last 4 percent in other chemical, special and miscellaneous uses.

Inside concrete, aggregate is the largest ingredient. FHWA says coarse and fine aggregates make up about 80 to 85 percent of a typical paving concrete mix by mass and 60 to 75 percent by volume, bound together by hardened cement paste. That is why the properties of the stone and sand have a large effect on how the concrete behaves; concrete and mortar ingredients goes through the mix. Beneath paving and slabs, graded crushed stone forms a compacted layer described on the crushed stone bases page, and loose gravel serves surfaces and drains, as in gravel for driveways and drainage. Anyone trying to make sense of how material is quantified and sold can start with reading a delivery ticket and measuring volume.

07The short version

Aggregates are hard, inert granular materials: natural sand and gravel shaped by weathering, crushed stone broken from quarried rock, and a growing but still small stream of recycled material. They are extracted, crushed, screened and sometimes washed before going mostly into concrete, asphalt, bases and fill. Figures here are American; your own country's geological survey or statistics office will have its local equivalents.